The six-port technology which up to recent years has been used for complex measurements of RF signals can also be used for receiving modulated or RF signals. Receivers built on the basis of the six-port technology act in the direct conversion manner allowing conversion from millimeter wave range in microwave range directly to the base band without any mixing to intermediate frequencies.
Technical details of six-port receiver and/or direct port receiver in general can be found, for example, in WO 099/33166. As the present invention is a further development of the N-port receiver technology, regarding the implementation of the elements building up the N-port receiver reference is explicitly made to said WO 099/33166 which is herewith incorporated by reference.
From EP 1011204 A1 a three-port junction receiver is known. This document proposes a direct receiver technique based on one power measurement and time multiplexing of input signals. This known technique bases on the passive linear three-port high frequency circuitry having two RF signal inputs and one output port attached to a power sensor. The signal output from the power sensor is low-pass filtered and then supplied to a DC-interface. This known technology, however, has the drawback that a RF-switch and at least one passive circuit having at least one passive shifter functionality must be provided.
Generally, millimeter-wave communication systems may play an important role in the future. The 60 GHz range is worldwide open for high data-rate short-range communication, where an operation bandwidth of approximately 4 GHz is allocated. When specifying an air-interface for said frequency range, the following constraints have to be coped with:
very high data rates (channel bandwidth up to 2 GHz),
simple RF direct down conversion also in a very high frequency rang, for example 60 GHz,
simple baseband processing (A/D converter with a low number of bits),
no complex signal processing and therefore small power consumption, and
minimum output back-of of the transmitter-power amplifier.
In consideration of these constraints, the modulation scheme has to be very simple which is compatible to the fact that usually the channel conditions are good. Depending on the application scenario, it is assumed that the channel conditions will be close to a Gaussian channel. This can result in a complete suppression of the need for equalization techniques in case a single-carrier approach is used.
In view of the above-captioned priorities is the object of the present invention to provide for a simplified down-conversion and demodulation technology for RF signals.
This object is achieved by means of the features of the independent claims. The dependent claims develop further the central idea of the present invention.
According to a first aspect of the present invention, a device for the down-conversion of a modulated RF signal without mixing stage is provided. The device comprises a linear two-port device having an input port for the RF signal to be down-converted as well as one output port. A single-power sensor is connected to the output port of the two-port device. The linear two-port device comprises a three-port junction having two inputs and one output connected to the power sensor. One input of the three-port junction is supplied with the RF signal. The other input of the three-port junction is supplied (without switching) with a further RF signal originating from a local oscillator. Alternatively, the other input of the three-port junction is supplied with a further RF signal being derived (branched-off) from the RF signal to be down-converted.
The linear two-port can comprise a three-port junction with one output to the power sensor, a first input for the RF signal to be downconverted and a second input for a RF signal branched off the RF signal to be downconverted, wherein the branching-off is effected by means of a power splitter.
A switch can be provided to selectively interrupt the branched-off RF signal.
A calculation unit can be provided for calculating the power of the RF signal to be downconverted during a time period in which the switch is in an interrupt state and therefore no branched-off RF signal is supplied to the second input of the three-port junction.
The RF signal branched off the RF signal to be downconverted can be passed through a processing unit such as a delay unit before being supplied to the second input of the three-port junction.
The delay unit can provide for a delay corresponding to the equivalent of an integer multiple of half the wave length of the carrier frequency of the RF signal to be downconverted.
The delay unit can provide for a delay corresponding to an integer multiple of a modulation state time duration of the RF signal to be downconverted.
The processing unit can comprise frequency dividing and frequency multiplying means. The division three-multiplication factor of the frequency dividing in frequency multiplying means can thereby be equal.
An automatic gate control unit for the RF signal to be downconverted can be connected to the input of the linear two-port device.
According to a further aspect of the present invention, a demodulator comprising such a device for the downconversion of a modulated RF signal without mixing stage is proposed. The demodulator comprises an analogue processing device connected to the output of the power sensor to detect the modulation states of the RF signal based on the output signal of the power sensor.
The analogue processing device can comprise an averaging as well as a hard decision unit. The hard decision unit outputs the detected modulation states of the downconverted modulated RF signal.
The demodulator can be particularly designed for demodulation of a BPSK modulated RF signal.
According to a still further aspect of the present invention, a method for the downconversion of a RF signal without mixing stage is proposed. Thereby the RF signal to be downconverted is supplied to a first input of a three-port junction. A further signal is supplied to the other input of the three-port junction. Thereby the further RF signal can originate either from a local oscillator and is supplied without switching to the other input of the three-port junction or the further RF signal is derived from the RF signal to be downconverted. Finally, the power of the output signal supplied at the output port of the three-port junction is sensed.
The further RF signal can be branched off the RF signal to be downconverted, processed and then supplied to the three-port device combining it with the RF signal to be downconverted.
The branched-off RF signal can be selectively interrupted.
The power of the RF signal to be downconverted can be calculated during a time period in which the branched-off RF signal is interrupted and therefore not supplied to the three-port junction.
The step of processing can comprise the step of delaying the branched-off RF signal before supplying it to the three-port junction.
The delay of the delay-step can correspond to the equivalent of an integer multiple of half wave lengths of the carrier frequency of the RF signal to be downconverted.
The delay can correspond to an integer multiple of a modulation state time duration of the RF signal to be downconverted.
The step of processing can comprise the steps of frequency dividing and frequency multiplying the branched-off signal.
The division/multiplication factor of the frequency-dividing and frequency-multiplying step can be equal.
The sensed power of the output of the three-port junction can be processed in an analogue manner to detect the modulation states of the RF signal.
The analogue processing steps thereby can comprise an averaging step as well as a hard- decision step.
The RF signal can be a BPSK modulated RF signal.